2 Answers
2

(1) The relation between User and ActivationLink is not entirely clear as presented.

An ActivationLink must have a User (i.e. be related to one and only one user)

However, how many ActivationLinks can a User have? Zero, One, Zero or more, One or more?

It is probably an identifying relationship, but I'd like to know a bit more before comitting to it.

(2) Correct. Users and Locations are (as you have described here) separate entities.

(3) Based solely on the typical meanings derived from the words used, one would assume that "A User can be a Student or a Workder", so they sound like subtypes... but this cannot be proved or disproved by the information at hand. Followup questions are:

Can thre be Students or Workers who are not Users?

Must a User be either a Student or a Worker?

Can a User be both a Student and a Worker?

Alternatively, if neither, what is a User? Is there a third (or fourth or fifth or...) table indicating what kind or type of User this is?

thanks Philip. An user have zero (after confirmed the link can be deleted) or one activationLink. Each user have an specific and unique activationLink. 3)Worker and student are a subtype of users. A user must be a student, worker or student/worker. An user only exists if has one of these categories. Is mandatory. thanks again
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anvdMay 4 '11 at 14:36

"-The relation between the users and activationLink is an identifying relationship because the specific activationLink only exists if the user is registered in the system."

Hmmmmmmmmmmmm. So the definition is then that a relationship between x and Y is "identifying" if the Y cannot exist "without the X" ?

That's not exactly what I remember from when I was taught. I think I've been told that a relationship is "identifying" if the relationship itself is (necessarily ?) part of the key/identifier (of the "child" entity). That is, that the attributes of the logical key/identifier of the parent entity are also part of the logical key/identifier of the child entity. Is this the case in your example ? Are activationlinks not unique by and of themselves ? Can several distinct users "share" the same activationlink ? Sounds odd.

Note that this definition makes the concept superficial, if not completely inapplicable, to relationships that do not have a "many" on at least one of its sides (such as your user-worker relationship, e.g.).

at the moment in my diagram. the relation between users and activation link is 1:1. The activationLink have a foreignKey of table users and is a identified relationship. Is wrong?
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anvdMay 4 '11 at 15:06